Electronics > Beginners

LM317AHVT and Heatsink

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mike_mike:
Can someone please recommend a schematic that sink current from the power supply ?
I need it for establishing the minimum current from this power supply to about 15mA. The current sink circuit will be used as minimum load.
The problem is that I did not found any current sink circuit that works starting from 1.25V ...

MarkF:
The current source that I can remember is the LM334.  It is 1 to 40V and 10mA max.

The minimum load for the LM317 is 10mA which the LM334 can satisfy.
You do not need to have 15mA.

Zero999:

--- Quote from: mike_mike on December 13, 2019, 09:05:17 pm ---Can someone please recommend a schematic that sink current from the power supply ?
I need it for establishing the minimum current from this power supply to about 15mA. The current sink circuit will be used as minimum load.
The problem is that I did not found any current sink circuit that works starting from 1.25V ...

--- End quote ---
There is no need for a current sink with this circuit, because R4 draws a steady 12.5mA from the LM317AHVT's output, which is above the worst case minimum load requirement of 12mA, stated in the data sheet.
https://www.onsemi.com/pub/Collateral/LM317AHV-D.pdf

mike_mike:
I tested the attached schematic to see if the output voltage rise when the transformer is unplugged from the mains.
The result was that the voltage does not rise when powering a load that sink a current which is below the maximum output current.
If the load sink more current than the maximum output current then when unplugging the transformer from the mains then the output voltage rise.
I made the above mentioned tests using LM317 AHVT from On Semiconductor. Will the behavior of the circuit remain the same if I will use LM317T instead of LM317AHVT ?
 

not1xor1:

--- Quote from: mike_mike on December 14, 2019, 04:11:36 pm ---I tested the attached schematic to see if the output voltage rise when the transformer is unplugged from the mains.
The result was that the voltage does not rise when powering a load that sink a current which is below the maximum output current.
If the load sink more current than the maximum output current then when unplugging the transformer from the mains then the output voltage rise.
I made the above mentioned tests using LM317 AHVT from On Semiconductor. Will the behavior of the circuit remain the same if I will use LM317T instead of LM317AHVT ?

--- End quote ---

You might put a 1-2k 2W resistor in parallel to C2. That might solve the problem.

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